1. Technical Field
Devices for fabrication of three-dimensional objects from powder starting materials.
2. Description of Related Art
Various methods have been proposed to produce information containing documents (text and graphics) through the direct deposition of charged powder onto a substrate such as paper. The direct powder deposition methods enable a simpler process than those generally used in printers that use electrographic technologies. Direct powder deposition methods for producing documents typically require a set of 100 to 600 staggered apertures per inch for pixel level deposition of the powder. Direct powder deposition printing systems have not been commercially successful to date due in large part to inadequate image quality.
Among the relevant patents which disclose direct powder deposition printing of documents are U.S. Pat. No. 3,689,935 of Pressman et al., U.S. Pat. No. 4,491,855 of Fujii et al., U.S. Pat. No. 4,568,955 of Hosoya et al., U.S. Pat. No. 4,743,926 of Schmidlin et al., U.S. Pat. No. 5,038,159 of Schmidlin, et al., the disclosures of which are incorporated herein by reference. In general, these patents disclose controlling the deposition of powder by an aperture electrode structure positioned between a charged powder (toner) source and a print receiving medium.
A number of other similar patents disclose controlling the electric field around each aperture with an electrode structure that has only the control electrode on an insulating support layer in close proximity to the toner source. Among the relevant patents which disclose related teachings are U.S. Pat. No. 5,036,341 of Larsson, U.S. Pat. No. 5,121,144 of Larson et al., and U.S. Pat. No. 5,812,160 of Wada et al., the disclosures of which are incorporated herein by reference.
Additionally, certain publications have disclosed summaries and/or advances in direct printing technology, including “TonerJet Tandem Color has Reached Prototype Stage” of Sandberg in the conference proceedings of the Society for Imaging Science and Technology (IS&T), NIP14: 1998 International Conference on Digital Printing Technologies, pp. 180-183; “Dot Formation by Toner Beam from Toner Cloud” of Hoshino et al. in the conference proceedings of IS&T, NIP15: 1999 International Conference on Digital Printing Technologies, pp. 598-600; and “Dot Formation Conditions from the Conductive Toner Cloud by Aperture Electrodes” of Zhou et al. in the conference proceedings of IS&T, NIP21: 2005 International Conference on Digital Printing Technologies, pp. 610-613.
In all of the above cited patents and publications, the general intent of the literature is to disclose various concepts for pixel level control of direct powder deposition onto an information carrier medium such as paper. The concepts require a source of toner (charged particles) and a control electrode structure with apertures in close proximity to the toner source. The spacing between the toner source and control electrode structure is a critical parameter that needs to be well-controlled to achieve high image quality. To obtain a well-controlled spacing in the gap between the toner source and control electrode, single component (toner only) development systems and their variants have been used for direct electrostatic deposition printers.
Two-component magnetic brush development systems (i.e., those that have a mixture of toner and magnetic carrier beads that triboelectrically charge the toner) have been widely used in electrophotography for in-contact development of electrostatic latent images formed by either light exposure of charged photoreceptors or gaseous ion controlled deposition onto an electroreceptor. For full-color electrophotographic systems that accumulate the color separations on the photoreceptor through a multiple photoreceptor recharge, expose and develop (READ) process, the development system must be non-interacting to prevent the scavenging and disturbance of previously deposited toner images. Various out-of-contact magnetic brush development systems and materials have been proposed to enable READ full color systems, but have not been commercially adopted due to the difficulties in controlling and maintaining the magnetic brush height. It is also for this reason that out-of-contact magnetic brush development systems have not been proposed for use in direct electrostatic deposition printers.
The carrier beads used in two-component magnetic brush development systems can be made from either soft magnetic or permanently magnetized materials. For soft magnetic carrier beads, the beads can be magnetized by a magnetic field but become essentially unmagnetized in the absence of a magnetic field. The magnetic brush development systems that use such two-component developer mixtures typically have stationary magnets inside a rotating sleeve that provide transport of the developer mixture to the development zone. For developer mixtures that use permanently magnetized carrier beads, the bead materials are selected to become permanently magnetized when subjected to a high magnetic field during a manufacturing process. When two-component developer mixtures with the permanently magnetized carrier beads are used in a magnetic brush development system, rotating magnets inside a stationary or rotating cylinder cause the transport of developer to the development zone. The rotating magnets acting on the permanently magnetized carrier beads causes additional mechanical agitation of the developer mixture that results in the release of some air borne toner.
Among the relevant patents which disclose the use of permanently magnetized materials in magnetic development systems are U.S. Pat. No. 4,546,060 issued to Miskinis et al., and U.S. Pat. No. 5,409,791 of Kaukeinen, et al., the disclosures of which are incorporated herein by reference. Additionally, the publication “Characterization of Toner Adhesion to Carrier: A Phenomenological Model” of Maher in the conference proceedings of IS&T, NIP10: 1994 International Conference on Digital Printing Technologies, pp. 156-159, discloses a method for measuring the charge-to-mass ratio of toner mixed with permanently magnetic carrier beads.
The patents and literature cited above describe a wide variety of digital printing technologies for printing information via the controlled placement of charged powder at a resolution of 200 to 800 dots per inch. The high resolution is necessary for printing text and graphics. In recent years, digital printing technologies have been applied to the fabrication of various 3D objects and 2D devices such as printable electronic circuits. For the most part, ink jet printing technologies are particularly well suited for such applications. However, ink jetting printing is an inherently slow process due to the need to scan ink jet heads over the substrate. Furthermore, the materials composition of the ink sometimes has undesired consequences on the final product.
It is for these reasons that powder based methods have been used for rapid building of devices and materials with particular desired characteristics. A number of patents disclose such methods for rapidly building objects, including U.S. Pat. No. 4,863,538 of Deckard, U.S. Pat. No. 5,204,055 of Sachs et al., and U.S. Pat. No. 6,206,672 of Grenda, the disclosures of which are incorporated herein by reference.
The above disclosures notwithstanding, problems remain unsolved in the fabrication of three-dimensional objects via powder-based fabrication processes. What is needed is an apparatus and method that enable precise and rapid transport and deposition of powders in three-dimensional patterns to thereby form three-dimensional objects.